The teeth upon the rotor breaker rings of a grinding apparatus of the above-described type are customarily secured in place by threaded bolts that extend generally parallel to the direction of rotation of the rotor and that have polygonal heads which are exposed during operation of the apparatus to damaging engagement with the material being ground. Additionally, the bolts are subjected to bending stresses when lateral forces are imposed upon the teeth secured thereby. Due to the environment within which they operate, the rotor teeth become worn or damaged during use, and must be periodically removed for purposes of repair or replacement. When the tooth-securing bolts have become deformed during use of the apparatus, removal of them and of the teeth can be quite tedious and time-consuming. This increases the amount of undesirable "down time" of the apparatus, and thus its operating cost.